This fourth edition of the World Health Organization's Guidelines for Drinking-water Quality builds on over 50 years of guidance by WHO on drinking-water quality, which has formed an authoritative basis for the setting of national regulations and standards for water safety in support of public health.

It is the product of significant revisions to clarify and elaborate on ways of implementing its recommendations of contextual hazard identification and risk management, through the establishment of health-based targets, catchment-to-consumer water safety plans and independent surveillance. It reflects the renewed focus on primary prevention.

Significant additional guidance on good practice is presented, incorporating changes introduced by the first and second addenda to the third edition. Emerging water management issues are comprehensively addressed for a range of circumstances, from household water treatment and safe storage and the bulk supply of water over long distances to the potential implications of climate change.

Additional risk assessments are presented for a number of new chemical and microbial hazards and applied to a suite of pesticides used for public health purposes. Existing reviews on chemicals and waterborne pathogens have been revised to account for new scientific information. The chapter on radiological aspects of drinking-water quality has been comprehensively updated.

Even more than the previous edition, this new edition emphasizes achievable practices and the formulation of sound regulations, applicable to low-income, middle-income and industrialized countries alike, that aim to prevent a potential health crisis caused by the consumption of unsafe drinking-water, against the backdrop of rapid urbanization, water scarcity and climate change.